Gastrulation:

Introduction

The basic body plan is established, including the physical
construction of the rudimentary primary
body axes.

As a result of the movements of gastrulation, cells are brought
into new positions, allowing them to interact with cells that
were initially not near them. This paves the way for inductive interactions, which
are the hallmark of neurulation
and organogenesis.

A morphed sequence of drawings from the classic staged diagrams
of Nieuwkoop and Faber (19??). This morph was generated and
kindly provided by Dr. Steve Black, Reed College.